FortranCInterface: Add support for LLVMFlang mangling

The following module.f90 file

module mymodule
contains
  subroutine mysub()
  end subroutine
end module

when compiled with flang-new (from LLVM 15.0.0) generate the _QMmymodulePmysub symbol.

$ flang-new -c module.f90
$ nm module.o
0000000000000000 T _QMmymodulePmysub

This commit fixes the regular expressions accordingly.

Issue: #22387 (closed)
Backport: release
Topic-rename: FortranCInterface-LLVMFlang